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/***
*atan.c - arctangent of x and x/y** Copyright (c) 1991-2001, Microsoft Corporation. All rights reserved.**Purpose:**Revision History:* 8-15-91 GDP written* 12-30-91 GDP support IEEE exceptions* 3-27-92 GDP support UNDERFLOW* 02-06-95 JWM Mac merge* 10-07-97 RDL Added IA64.********************************************************************************/
#include <math.h>
#include <trans.h>
#if defined(_M_IA64)
#pragma function(atan, atan2)
#endif
static double _atanhlp(double x);
static double const a[4] = { 0.0, 0.52359877559829887308, /* pi/6 */ 1.57079632679489661923, /* pi/2 */ 1.04719755119659774615 /* pi/3 */};
/* constants */static double const EPS = 1.05367121277235079465e-8; /* 2^(-53/2) */static double const PI_OVER_TWO = 1.57079632679489661923;static double const PI = 3.14159265358979323846;static double const TWO_M_SQRT3 = 0.26794919243112270647;static double const SQRT3_M_ONE = 0.73205080756887729353;static double const SQRT3 = 1.73205080756887729353;
/* chose MAX_ARG s.t. 1/MAX_ARG does not underflow */static double const MAX_ARG = 4.494232837155790e+307;
/* constants for rational approximation */static double const p0 = -0.13688768894191926929e+2;static double const p1 = -0.20505855195861651981e+2;static double const p2 = -0.84946240351320683534e+1;static double const p3 = -0.83758299368150059274e+0;static double const q0 = 0.41066306682575781263e+2;static double const q1 = 0.86157349597130242515e+2;static double const q2 = 0.59578436142597344465e+2;static double const q3 = 0.15024001160028576121e+2;static double const q4 = 0.10000000000000000000e+1;
#define Q(g) (((((g) + q3) * (g) + q2) * (g) + q1) * (g) + q0)
#define R(g) ((((p3 * (g) + p2) * (g) + p1) * (g) + p0) * (g)) / Q(g)
/***
*double atan(double x) - arctangent**Purpose:**Entry:**Exit:**Exceptions:* P, I\*******************************************************************************/double atan(double x){ uintptr_t savedcw; double result;
/* save user fp control word */ savedcw = _maskfp();
/* check for infinity or NAN */ if (IS_D_SPECIAL(x)){ switch(_sptype(x)) { case T_PINF: result = PI_OVER_TWO; break; case T_NINF: result = -PI_OVER_TWO; break; case T_QNAN: return _handle_qnan1(OP_ATAN,x,savedcw); default: //T_SNAN
return _except1(FP_I,OP_ATAN,x,_s2qnan(x),savedcw); } }
if (x == 0.0) RETURN(savedcw,x);
result = _atanhlp(x); RETURN_INEXACT1(OP_ATAN,x,result,savedcw);}
/***
*double atan2(double x, double y) - arctangent (x/y)**Purpose:**Entry:**Exit:**Exceptions:* NAN or both args 0: DOMAIN error*******************************************************************************/double atan2(double v, double u){ uintptr_t savedcw; double result;
/* save user fp control word */ savedcw = _maskfp();
/* check for infinity or NAN */ if (IS_D_SPECIAL(v) || IS_D_SPECIAL(u)){ if (IS_D_SNAN(v) || IS_D_SNAN(u)){ return _except2(FP_I,OP_ATAN2,v,u,_d_snan2(v,u),savedcw); } if (IS_D_QNAN(v) || IS_D_QNAN(u)){ return _handle_qnan2(OP_ATAN2,v,u,savedcw); } if ((IS_D_INF(v) || IS_D_MINF(v)) && (IS_D_INF(u) || IS_D_MINF(u))){ return _except2(FP_I,OP_ATAN2,v,u,QNAN_ATAN2,savedcw); } /* the other combinations of infinities will be handled
* later by the division v/u */ }
if (u == 0) { if (v == 0) { return _except2(FP_I,OP_ATAN2,v,u,QNAN_ATAN2,savedcw); } else { result = PI_OVER_TWO; } } else if (INTEXP(v) - INTEXP(u) > MAXEXP - 3) { /* v/u overflow */ result = PI_OVER_TWO; } else { double arg = v/u;
if (ABS(arg) < D_MIN) {
if (v == 0.0 || IS_D_INF(u) || IS_D_MINF(u)) { result = (u < 0) ? PI : 0; if (v < 0) { result = -result; } if (result == 0) { RETURN(savedcw, result); } else { RETURN_INEXACT2(OP_ATAN2,v,u,result,savedcw); } } else {
double v1, u1; int vexp, uexp; int exc_flags;
//
// in this case an underflow has occurred
// re-compute the result in order to raise
// an IEEE underflow exception
//
if (u < 0) { result = v < 0 ? -PI: PI; RETURN_INEXACT2(OP_ATAN2,v,u,result,savedcw); }
v1 = _decomp(v, &vexp); u1 = _decomp(u, &uexp); result = _add_exp(v1/u1, vexp-uexp+IEEE_ADJUST); result = ABS(result);
if (v < 0) { result = -result; }
// this is not a perfect solution. In the future
// we may want to have a way to let the division
// generate an exception and propagate the IEEE result
// to the user's handler
exc_flags = FP_U; if (_statfp() & ISW_INEXACT) { exc_flags |= FP_P; } return _except2(exc_flags,OP_ATAN2,v,u,result,savedcw);
} }
else { result = _atanhlp( ABS(arg) ); }
}
/* set sign of the result */ if (u < 0) { result = PI - result; } if (v < 0) { result = -result; }
RETURN_INEXACT2(OP_ATAN2,v,u,result,savedcw);}
/***
*double _atanhlp(double x) - arctangent helper**Purpose:* Compute arctangent of x, assuming x is a valid, non infinite* number.* The algorithm (reduction / rational approximation) is* taken from Cody & Waite.**Entry:**Exit:**Exceptions:********************************************************************************/static double _atanhlp(double x){ double f,g,result; int n;
f = ABS(x); if (f > MAX_ARG) { // if this step is ommited, 1.0/f might underflow in the
// following block
return x > 0.0 ? PI_OVER_TWO : -PI_OVER_TWO; } if (f > 1.0) { f = 1.0/f; n = 2; } else { n = 0; }
if (f > TWO_M_SQRT3) { f = (((SQRT3_M_ONE * f - .5) - .5) + f) / (SQRT3 + f); n++; }
if (ABS(f) < EPS) { result = f; } else { g = f*f; result = f + f * R(g); }
if (n > 1) result = -result;
result += a[n];
if (x < 0.0) result = -result;
return result;}
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